No birthday three-peat for Ko

World golf No.1 Lydia Ko has failed to defend her title at the latest LPGA Tour event in San Francisco.

Lydia Ko Photo: Photosport

Chasing a third consecutive Swinging Skirts Classic trophy, Ko finished the final round tied for sixth at one-under for the tournament, eight strokes behind the runaway winner from Japan, Haru Nomura.

It wasn't a birthday to remember for the New Zealander, who celebrated turning 19 by battling windy conditions at the Lake Merced Golf Club to a three-over-par final round score of 75.

But Ko wasn't struggling alone, as only five players in the field were able to break par on day four.

Nomura battled her way to a closing 73 to finish at nine-under-par 279, increasing her three-shot overnight lead, but the final round was anything but a cakewalk for the 23-year-old from Yokohama.

Adding to her breakthrough Australian Open victory in February, Nomura joins Ko and South Korean Jang Ha-na as multiple winners early in the LPGA season.

Haru Nomura Photo: Photosport

South African Lee-Anne Pace (74) took second alone at five-under, with American Gerina Piller (73) and South Korean Choi Na-yeon (75) sharing third a shot further back.

Despite missing out on the title three-peat, Ko seemed happy with her performance.

"It was a pretty cool day. Obviously I would have like to shoot something crazy under par but it was tough and I felt I played pretty strong and made quite a few good up and downs on the back nine," she said.

"I'm happy with the way I finished this week and top-ten around here I'll take it."

Ko said tour officials, sponsors and the fans helped her celebrate her birthday.

"It's been really cool to have my birthday here the last three years. It's pretty cool when you're going down the fairway and they wish you happy birthday."

"The whole IMG team sung me happy bithday on the first tee and I said I don't know if I should get emotional or embarrassed."